The present invention relates to a method for producing an x-ray tube, and more particularly, to the method for producing the x-ray tube wherein a ceramic bulb, a ceramic stem, and an output window are brazed together using a brazing agent.
Japanese Patent Application Publication (Kokai) Nos. HEI-9-180630 (corresponding to U.S. patent application Ser. No. 09/113,372) and HEI-9-180660 (corresponding to U.S. patent application Ser. No. 09/113,371) disclose technologies in this field. In the disclosed method for producing the x-ray tube, at a position outside of a vacuum brazing oven, a stem is set through a brazing agent at one end of a bulb, and an output window is set through a brazing agent at another end of the bulb. The thus pre-assembled x-ray tube is conveyed into the vacuum brazing oven, and the oven is heated at high temperature for melting the brazing agent after the oven is evacuated to 1xc3x9710xe2x88x926 Torrs. Thus, a combination of the bulb, the stem and the output window provides a sealed vessel in the oven. Thereafter, the x-ray tube is taken out from the oven, and then, further evacuation is carried out with respect to an inside of the sealed vessel through a discharge pipe provided at the stem to provide high vacuum condition. Then, the discharge pipe is plugged. In this way, connection of components using the brazing agent improves assembleability of the x-ray tube.
However, the following problems remain in the conventional x-ray tube due to the above-described production method.
That is, for connecting each component of the x-ray tube with brazing, high vacuum is provided in the oven and the brazing agent is melted by heating the oven. Upon completion of the brazing, the assembled x-ray tube is taken out from the oven, and high vacuum is again provided in the sealed vessel through the discharge pipe. Accordingly, the evacuation process is performed twice, which is a task to be solved for improving an efficiency of assembly of the x-ray tube.
It is an object of the present invention to overcome the above-described problems and to provide a method for producing the x-ray tube capable of improving assembling efficiency thereof.
To attain the above described object, the present invention provides a method for producing an x-ray tube which includes a sealed vessel provided with a bulb having one open end and another open end, a stem fixed to the one open end of the bulb through a first brazing agent, and an output window fixed to the another open end of the bulb through a second brazing agent, a filament disposed in the sealed vessel for emitting electrons, and a focussing electrode disposed in the sealed vessel and surrounding the filament, incidence of the electron from the filament into the output window providing x-ray discharge outwardly through the output window, the method comprising the steps of;
interposing a flange portion of the focussing electrode between the bulb and the stem, the flange portion having an outer peripheral end portion provided with a skirt portion where a gas discharge port allowing an inside of the bulb to communicate with an outside is formed;
positioning a projecting portion of the first brazing agent between the stem and the flange portion of the focussing electrode for maintaining the stem away from the flange portion, and positioning a third brazing agent between the flange portion and the bulb, and positioning the second brazing agent between the bulb and the output window to provide a temporary assembly of the x-ray tube; and
disposing the temporary assembly of the x-ray tube in a vacuum brazing oven, and discharging gas from an inside space of the vessel defined by the bulb, the stem and the output window through a gap between the flange portion and the stem, the gap being provided by the projecting portion of the first brazing agent.
According to the above-described method for producing the x-ray tube, the gap is positively provided between the stem and the flange portion by interposing the projecting portion of the first brazing agent between the stem and the flange portion. Thus, gas inside the bulb can be discharged through the gap in the vacuum brazing oven. While the discharge of gas from the inside space is continued, the projecting portion of the first brazing agent, the first brazing agent, the second brazing agent and the third brazing agent are melted by increasing the temperature of the vacuum brazing oven to a predetermined temperature to perform brazing connection between the flange portion and the stem, between the bulb and the flange portion, and between the bulb and the output window. In this way, brazing connection is completed in the vacuum brazing oven while maintaining the sealed vessel in a high vacuum condition without provision of a discharge pipe in the stem. That is, the x-ray tube without the gas discharge pipe can be fabricated with an advantage that the assembly of the x-ray tube is completed concurrently with the take-out of the x-ray tube from the vacuum brazing oven.
Further, gas discharge is achieved through the gap between the stem and the flange portion of the focussing electrode, and the flange portion of the focussing electrode is interposedly fixed between the bulb and the stem by melting the first and third brazing agents in the vacuum brazing oven. Consequently, the focussing electrode can be easily and stably fixed to the sealed vessel.
Furthermore, positioning of the focussing electrode with respect to the stem can be easily and reliably performed by simply positioning the stem into the skirt portion during assembly of the x-ray tube. Further, gas in the sealed vessel can be smoothly discharged through the gas discharge port formed in the skirt portion. That is, gas discharge from the sealed vessel can be assured by forming the gas discharge port in the skirt portion irrespective of the provision of the skirt portion at the focussing electrode.
In this case, preferably, the gas discharge port is positioned in association with the projecting portion of the first brazing agent. With this arrangement, since the gap between the bulb and the stem is stably provided by the projecting portion, more stable gas discharge is achievable by the alignment between the projecting portion and the gas discharge port.
Preferably, the projecting portion provided at the first brazing agent is formed of a material identical with the material of the first brazing agent. In this case, the first brazing agent is formed of a ring shaped sheet like member, and the projecting portion comprises an upright pawl formed by cutting a part of the first brazing agent and folding the cut part. By providing the projecting portion in this fashion, it is unnecessary to provide a separate projecting portion to the ring like main body of the brazing agent. The projecting portion can be easily provided as an upright pawl by forming L-shaped or U-shaped slit in the main body of the brazing agent and by folding the slitted part.
In the above described production method, preferably, the second brazing agent can have a projecting portion which spaces the output window away from the bulb to provide a gap through which gas discharge can be performed. With this arrangement, gas discharge at the both open ends of the bulb can be performed, to thus further promote gas discharge.
Similar to the projecting portion of the first brazing agent, the projecting portion at the second brazing agent is preferably formed of a material identical with the material of the second brazing agent. Further, the second brazing agent is preferably formed of a ring shaped sheet like member, and the projecting portion of the second brazing agent comprises an upright pawl formed by cutting a part of the second brazing agent and folding the cut part.
Preferably, a cap surrounding the output window is provided, and the output window is interposed between the bulb and the cap, and the second brazing agent is positioned between the bulb and the output window, and a fourth brazing agent is positioned between the output window and the cap. The second brazing agent has a projecting portion spacing the output window away from the bulb to provide a gap through which gas discharge is performed. With this arrangement, the output window can be interposed between the cap and the bulb by melting the second and fourth brazing agents in the vacuum brazing oven. Thus, the cap can protect the output window and can stably fix the output window.
Preferably, the cap includes a sleeve portion surrounding the end portion of the bulb and the sleeve portion is formed with a gas discharge port allowing an inside of the bulb to communicate with an outside. With this arrangement, the positional relationship among the output window, the cap and the bulb can be simply and stably determined by positioning the output window and the end portion of the bulb into the sleeve portion of the cap during assembly of the x-ray tube. Further, gas discharge out of the sealed vessel can be smoothly achieved through the gas discharge port formed in the sleeve portion. That is, stable gas discharge is achievable by forming the gas discharge port in the sleeve portion irrespective of the provision of the sleeve portion at the cap.
Preferably, the gas discharge port of the cap is positioned in association with the projecting portion of the second brazing agent. With this arrangement, more stable gas discharge can be achieved by the alignment between the projecting portion and the gas discharge port because the gap between the bulb and the output window can be stably maintained by the projecting portion.
Further, the present invention provides a method for producing an x-ray tube which includes a sealed vessel provided with a bulb having one open end and another open end, a stem fixed to the one open end of the bulb through a first brazing agent, and an output window fixed to the another open end of the bulb through a second brazing agent, and a filament disposed in the sealed vessel for emitting electrons, incidence of the electrons into the output window providing x-ray discharge outwardly through the output window, the method comprising the steps of;
interposing the output window between the bulb and a cap surrounding the output window, the cap having a sleeve portion surrounding the end portion of the bulb, the sleeve portion being formed with a gas discharge port which communicates the inside of the bulb with the outside,
positioning the first brazing agent between the bulb and the stem, positioning a projecting portion of the second brazing agent between the bulb and the output window, and positioning a fourth brazing agent between the output window and the cap to provide a temporary assembly of the x-ray tube where the output window is spaced away from the bulb, and
disposing the temporary assembly of the x-ray tube in a vacuum brazing oven, and discharging gas from an inside space of the vessel defined by the bulb, the stem and the output window through a gap between the bulb and the output window, the gap being provided by the projecting portion of the second brazing agent.
According to the above described method for producing the x-ray tube, the gap is positively provided between the output window and the bulb by interposing the projecting portion of the second brazing agent between the output window and the bulb. Thus, gas inside the bulb can be discharged through the gap in the vacuum brazing oven. While the discharge of gas from the inside space is continued, the first brazing agent, the projecting portion of the second brazing agent, the second brazing agent and the fourth brazing agent are melted by increasing the temperature of the vacuum brazing oven to a predetermined temperature to perform brazing connection between the bulb and the stem and between the bulb and the output window. In this way, brazing connection is completed in the vacuum brazing oven while maintaining the sealed vessel in a high vacuum condition without provision of a discharge pipe in the stem.